While taking pictures or shooting a film, a camera or Digital Video (DV) is generally supported by a tripod through which shooting angle, height and balance can be adjusted. In most of tripods, the adjustments are achieved by telescopic stand legs which are controlled by locking units for their leg tubes. Due to different designs, most of the tripods have different locking units. However, the tripods of this kind are generally provided with a plurality of locking units which need to be locked simultaneously to fix the multistage leg tubs. Without a safety device, the locking units may be released by accident after the angle and the height of the tripods were fixed. Thus, the relative sliding between the leg tubs may lead to changes of angle and height, even damages of the photographic equipments.